It has long been recognized that one of the most valuable products generated through the refining of crude mineral oils is lubricating oils. It is common practice to recover lubricating oil basestocks by solvent extracting, with a selective solvent, undesirable components such as sulfur compounds, oxygenated compounds, and aromatics from straight distillates. However, with the decline in the availability of paraffinic base crudes, and a corresponding increase in the proportion of naphthenic and asphaltic base crudes, it is becoming increasingly difficult to meet the demand for lubricating oil basestocks, or base oils. For example, American Petroleum Institute (API) requirements for Group II basestocks include a saturates content of at least 90%, a sulfur content of 0.03 wt. % or less and a viscosity index (VI) between 80 and 120. Thus, there is a trend in the lube oil market to use Group II basestocks instead of Group I basestocks in order to meet the demand for higher quality basestocks that provide for increased fuel economy, reduced emissions, etc.
Conventional techniques for preparing basestocks such as hydrocracking or solvent extraction require severe operating conditions such as high pressure and temperature or high solvent:oil ratios and high extraction temperatures to reach these higher basestock qualities. Either alternative involves expensive operating conditions and low yields.
Hydrocracking has been combined with hydrotreating as a preliminary step. However, this combination also results in decreased yields of lubricating oils due to the conversion to distillates that typically accompany the hydrocracking process.
Thus, as the demand for quality lube oil basestock continues to increase, the search for new and different processes, catalysts, and catalyst systems that exhibit improved activity, increased yields, selectivity and/or longevity is a continuous, ongoing exercise. Therefore, there is a need in the lube oil market to provide processes that can produce lube oil basestocks that meet the demand for increased fuel economy, reduced emissions, etc.